Transcript for Investigation Impact: Miners Get Another Shot at Black Lung Benefits

Tonight a year-long investigation yields some stunning results that could change everything for a group of coal miners suffering from black lung disease. Here's ABC's chief investigative correspondent Brian Ross for our series "Nightline" investigates. Reporter: New hope in coal country for miners suffering from debilitating disease called black lung. Hope for men like Mac lester. Shortness of breath. Reporter: And Steve day. My lung is shot. Reporter: And Wayne cordal. Those miners and hundreds of others were denied benefits after negative X ray Readings by one doctor at John Hopkins hospital, Dr. Paul wheeler, an ABC news investigation last year conducted with center for public integrity found of 1,573 cases, Dr. Wheeler on behalf of coal companies never found a single case of severe black lung in any coal miner. Not one. I have no idea what happens once the x-rays leave my department. Reporter: Does it matter to you? It would matter to me if I was wrong. No one has proven to me I was wrong. Reporter: Our investigation found he has been wrong a lot. Based on 100 cases of miners in which autopsies or biopsies later found black lung after Dr. Wheeler had not. Days after our broadcast last October, Johns Hopkins suspended Dr. Wheeler's black lung program. Now the department of labor which administers the miners' benefits program is taking more significant action because of our investigation. It was shocking. Reporter: The labor department's top lawyer solicitor Patricia smith said this week officials in the program have been order in this directive to not credit Dr. Wheeler's negative Readings in black lung cases. My judgment of his credibility, unless some one can convince us otherwise that anyone who has done that many Readings and never found black lung isn't probably credible. In coal country hundreds of miners. Something she says, officials at the labor department did not realize until after watching the ABC news report. Was the labor department unaware of Dr. Wheeler's one-sided findings over so many years? As far as I know, yes. Reporter: For miners like Steve day who gave up hope after Dr. Wheeler ruled he did not have black lung, labor department said he can reapply and not worry about what Dr. Wheeler is going to say. If you feel that Dr. Wheeler's evidence was part of your case you should file a new claim. Those claims will be re-evaluated? Yes. Reporter: It happened after the case of Wayne cordal, of Richmond, Virginia, came to the attention of officials in Washington. It was a big letdown. A big letdown. Because I felt like I was entitled to it. Reporter: Even after the ABC news broadcast, cordal's claim was denied after a government claims examiner cited Dr. Wheeler's negative X ray Reading. What I noticed was the department of labor hadn't connected the dots. Reporter: ABC news brought cordal's case to the attention of congress and senator bob Casey and congressman George miller then demanded action in this letter to the secretary of labor about Dr. Wheeler's questionable and potentially unethical Prak tictice thousands. His tainted evidence continues through the cyst temperature to work against the miners. Reporter: A short time later the department of labor sent a directive about Dr. Wheeler to officials across the country just in time for the interview with ABC news earlier this week. How recently was that done? Today. Reporter: The labor department expects the big coal companies who relied on Dr. Wheeler so much for so many years and fight the decision and perhaps find others to replace him. Reporter: It send a signal the department of labor hasn't sent for a long time. They're not going to tolerate this kind of evidence. They're not going to tolerate a system that is rigged against people who often don't have much power. Reporter: Dr. Wheeler still maintains he made the right call on all the miners that he always follows what he says was the standard of care. As for the labor department director off dire directive of him and his credibility he told me by phone heap doesn't take it seriously because they're not doctors from qualified medical institutions look he says he is, juju. Thank you, Brian. Thank you so much for important reporting.

This transcript has been automatically generated and may not be 100% accurate.